Generally in the medical field, the endoscope has been used by inserting its thin and long insertion portion into a body cavity for the purpose of observing the internal organ within the body cavity such as the large intestine, or performing various types of treatment using the treatment instrument inserted into the treatment instrument channel if required. The insertion portion of the endoscope includes a distal end portion, a bending portion and a flexible tube portion in the order from the distal end.
When the insertion portion of the endoscope is inserted into the body cavity, the user, for example, the operator grasps the flexible tube portion to perform a predetermined operation of an operation knob provided on an operation portion of the endoscope while pushing the flexible tube portion into the body cavity such that the bending portion is bent toward a desired direction. The insertion portion of the endoscope has been made into various forms so as to be inserted into the body cavity further smoothly.
For example, the endoscope disclosed in Japanese Unexamined Patent Application Publication No. 58-49132 (Patent Document 1) has its distal end portion of the insertion portion provided with a first bending portion and a second bending portion connected in series in the order from the distal end portion. The first bending portion includes a series of plural bending pieces inside so as to be bent through the predetermined operation of the operation portion.
The insertion portion of the endoscope disclosed in Utility Model Application Publication No. 1-22641. (Patent Document 2) is provided with a first bending portion which can be externally bent toward four directions, and a readily flexural second bending portion provided with the stay coil and the node ring so as to be bent toward four directions, which are connected in series in the order from the distal end side.
When the insertion portion of the endoscope as disclosed in Patent Documents 1 and 2 passes the flexed portion within the body cavity, the second bending portion is bent while following the bending state of the first bending portion which has been subjected to the bending operation along the body cavity wall. The second bending portion of the endoscope may be bent at the smaller curvature radius than that of the first bending portion depending on the insertion condition. The second bending portion may abut on the body cavity wall under the force applied by the operator to push the insertion portion, and is brought into the state where a large flexed state is locally observed.
The second bending portion in the aforementioned flexed state presses the flexed body cavity wall which may be flexed further acutely in accordance with the force pushed by the operator. This may cause the second bending portion to be stuck with the acutely flexed body cavity. In the thus acutely flexed body cavity, the resistance of the body cavity wall against the second bending portion is increased to make it difficult for the insertion portion to be inserted into the flexed portion of the body cavity.
In the aforementioned case, unnecessarily excessive load is exerted to the body cavity to be stretched to the level more than necessary. This may impose not only the burden but also the pain on the patient who receives the endoscopic inspection.
In view of the aforementioned disadvantageous state, it is an object of the present invention to provide an endoscope which suppresses the resistance generated when the insertion portion passes a flexed portion of the body cavity during the endoscopic inspection so as to improve the insertion performance of the insertion portion, and to alleviate the burden and the pain imposed on the patient.